Telephone system



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TELEPHONE SYSTEM Filed Feb. '7, 19114 8 Sheets-Sheet 8 Y INVENTQIL HARRY N. fNEwsTAEDT ATroRNEY Patented May 8, 1945 TELEPHONE SYSTEM Harry N. Newstedt, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application February 7, 1944, Serial No. 521,347

39 Claims.

This invention relates in general to small private branch exchange telephone systems, but more particularly to private branch exchange telephone systems arranged for conference calls and having special signaling circuits for simultaneously signaling a plurality of lines.

The object of the present invention is to provide a, conference call arrangement whereby group conference calls may be set up by inserting the plug of a cord circuit into a group or subgroup jack and then simultaneously signaling all the subscribers lines associated with this group or subgroup jack.

Another object of the invention is to provide arrangements for including a predetermined number of lines in a main conference group and then provide progressively smaller subgroups of these lines for conference subgroups. That is, the main conference group includes, by way of example only, six subscribers lines, the next subgroup contains only four of these six subscribers lines and the last subgroup contains only two of the last four subscribers lines.

A further object of the invention is to provide a selective conference arrangement whereby the operator by tip touching the sleeves of the jacks of the subscribers lines desired in the conference may be selectively and simultaneously signaled and connected in a common conference circuit upon answering.

A feature of the invention relates to the provision of a special conference trunk whereby several groups of lines may be inter-connected for conference. Another feature relates to the circuit arrangements whereby any line in conference may retire from the conference at will and resume regular service.

Other objects and features of the invention will become apparent from the following description of the drawings in which Fig. 1 diagrammatically illustrates the telephone lines and inter-connections in a particular area, Fig. 2 diagrammatically illustrates an operators switchboard and the different lines of this area terminating therein, Figs. 3 and 4 illustrate one group of lines and their associated line equipment terminating at the operators switchboard, Fig. 5 shows the operators cord circuit, Figs. 6 and '7 show another group of lines and their associated line equipment terminating at the operators switchboard, and Fig. 8 shows a common conference circuit.

This telephone system is intended for` use in a fairly large area which includes an airfield with a number of long runways, an operations building, an administration building, other miscellaneous buildings including a guard house and a restricted area. Telephone sets are provided at strategic points around the boundary of this entire area and these telephone sets may be connected to individual telephone lines or to party lines as desired. A telephone line is provided for each runway of the airfield and telephone sets are provided for each line at predetermined points along each of the runways. A number of individual telephone lines are also provided in each of the different buildings for the different oiiices therein. A common telephone talking circuit is provided for the restricted area and the telephone sets in this area are divided into a plurality of groups, each such group having a separate signaling circuit. The guard house is provided with a telephone set connected to the common talking circuit of this area and may be individually signaled or signaled over the above mentioned separate group signaling circuits whenever a group in the restricted area is signaled.

All of these telephone lines and circuits extend by cable to the administration building where they terminate in switching keys which are connected by cable to the operations building where they terminate in similar switching keys which normally connect these lines through their line circuits to the manual switchboard in the operations building.

An emergency switchboard, which is a duplicate of the switchboard in the operations building, is provided at some other building somewhat remote from the operations building. Emergency cables connect the emergency switchboard to the switching keys in both the operations building and in the administration building. The telephone lines can be switched to this emergency board by means of the cables provided in case the main switchboard or certain cables are damaged.

Each telephone line terminates in a manual jack at the switchboard while the common talking circuit for the restricted area is multipled to a plurality of jacks, one for calling purposes and one for each separate group on this common talking circuit for signaling purposes. The runway telephone lines, in addition to their regular line jacks, are provided with a common jack for use when group signaling on all runway lines is desired. A similar common group signaling jack is provided for the telephone lines extending to the boundary posts, or substations. Some of the telephone lines in both the operations and administration buildings are divided into subgroups,

the first subgroup comprising certain telephone lines, the second subgroup comprising the same certain lines as in the rst subgroup and, in addition, other lines. Successive subgroups include all the lines of the preceding subgroups and certain additional lines. Finally a main group is provided which includes all of the lines in the preceding subgroups and further additional lines. A jack is provided at the switchboard for each of these subgroups and for the main group for group signaling the subgroup or main group of lines desired for conference. A conference trunk terminating in a plurality of jacks at the switchboard is provided to enable the operator to interconnect any of the lines of this system for conference purposes by means of the cord circuits at her position. A conference group key is provided at the operators position for each group of subscribers lines to enable the operator to provide a conference between a predetermined subgroup or group of lines. A conference select key is also provided for each group of subscribers lines to enable the operator to provide a conference between certain selected subscribers lines in a group.

Referring now to Fig. l, the circles at the outer edges of this iigure designate the boundary posts or the boundary telephone lines of this particular area. The lefthand dotted rectangle designates the operations building in which is provided telephone subscribers lines designated by circles, an operators switchboard designated S, and one of the line circuits designated LC. The righthand dotted rectangle designated Administration buildingf is also provided with a number of telephone lines designated by circles, such as A to D, inclusive. An air field is included in this area and a number of telephone lines extend parallel with these runways and the substations on these lines are shown as circles directly below the designation Runway Also included in this area is a restricted area which is provided with a common talking circuit. The subscribers lines connected to this common talking circuit are divided into three groups, each of which have their individual signaling circuits. The circles, such as I I, 2| and 3|, designate one of the substations in each of these three groups and the small rectangles, such as RII, R2I and RBI designate the ringers for these substations. A substation is also provided at the guard house, designated I0, and is also connected to this common talking circuit. The guard house may be individually signaled and is always signaled when any one of the lines in this group are signaled. An emergency switchboard is provided in one of the other buildings in this area and this switchboard is a duplicate of the switchboard in the operations building. All of the line conductors from the various telephone lines throughout this area extend to the administration building where they terminate in the switching key AS. Through back .contacts on switching key AS all of these lines are further extended to the operations building where they terminate in the switching key OS and from thence terminate in their respective line circuits LC and jacks at the operators switchboard. At make contacts of the switching keys AS and OS these lines can be extended by cable to the emergency switching key ES. In case the regular switchboard in the operations building is destroyed it would then be possible to continue the service from the emergency switchboard, in which case the switching keys AS and ES are operated to connect all of the lines of this area with the emergency switchboard. In

case the cable extending from the back contacts of switching key AS to back contacts of switching key OS should be destroyed or damaged the telephone lines in this area could be connected to the switchboard in the operations building by way of front contacts of switching key AS, back contacts of switching key ES, and front contacts of switching key OS.

In Fig. 2 the subscribers lines A to F, inclusive, in the administration building are shown terminating in line circuits LCA to LCF, inclusive, and jacks AJ I to AJ 6, inclusive, at the operators switchboard in the operations building. A main group jack GI and two subgroup jacks SBI and SBZ are shown for enabling the operator to set-up conference calls for these respective lines in the administration building. The detailed circuits for this group of lines in the administration building is shown in Figs. 3 and 4.

In the center of Fig. 2 is shown the conference circuits which are shown in detail in Fig. 8. These conference circuits are used by the operator to interconnect two groups of lines for conference purposes and are interconnected by way of the operators cord circuits CC. Fig. 2 also shows the conference keys which are thrown upwards when all of the subscribers in a group or subgroup are desired in a conference and which keys are thrown downwards when the operator selects only particular ones of the subscribers of a group for conference purposes. A similar set of line circuits and jacks are shown for terminating the telephone lines in the operations building. The telephone lines indicated as runway lines in the upper lefthand corner terminate in the operators switchboard in line circuits LC and jacks RJ I to RJ 5, inclusive. These runway lines have a conference group circuit terminating in the jack RG for enabling the runway telephone lines to be included in a conference call arrangement. The telephone lines around the outer extremity of this area terminate in line circuits and jacks BJI to BJ 5, inclusive, and are also provided with a common conference group jack BG. The telephones associated with the restricted area are shown in the lower lefthand corner of Fig. 2 and comprises the guard house telephone I0 and three groups of subscribers lines, such as II, 2| and 3| all of which are connected to a common talking circuit. Each of the three groups of telephones in this common talking area is provided with separate and individual signaling circuit. The jacks GH, SGI to SGS, inclusive, and jack G2 are associated with this common talking circuit. The jack GH is for use in signaling only the guard house IU and for use when any line in this group initiates a call. The jack SGI is for signaling only the rst subgroup of lines, the jack SG2 is for signaling only the second subgroup and the jack SG3 is for signaling only the third subgroup. The group G2 is used by the operator when al1 of the lines associated with this common talking circuit are to be signaled. The guard house is also signaled whenever another subgroup is signaled. The circuits for this restricted area is shown in detail in Figs. 6 and 7.

In Fig. 3 the administration subscribers line A is connected by way of line conductors 30| and 302 to the administration switching key AS, conductors 386 and 381, the operations building switching key OS, to the line circuit LC--A, which is individual to this line. The line circuit LC--A comprises a ring cut-oir relay 3|0, a conference relay 320, a line relay 330, a cut-off relay 340,

and a jack AJ I. Subscribers line B extends by way of line conductors 303 and 304 to the dotted portion, which indicates the switching keys similar to the keys shown for subscriber A, and terminating in a line circuit LC--B and jack AJ2. Line circuit LC-B also has a ring cut-off relay, a conference relay, a line relay and a cut-off relay corresponding to the relays in the line circuit LC-A. The subscribers lines C and D shown in Fig. 3 and the subscribers lines El and F shown in Fig. 4 are similarly connected to their individual line circuits which are identical with the line circuit LC-A. The subgroup jack SBI and associated relays 350 and 360 are used by the operator when it is desired to include substations A and B in a subgroup conference. The subgroup jack SBZ and its associated relays 450 and 460 are used by the operator when it is desired to include substations A, B, C and D in a subgroup conference. The main group jack GI and its associated relays 4I0 and 420 are used by the operator when it is desired to include all of the subscribers lines A to F, inclusive, in a group conference. The group conference key GC is operated by the operator to control relay 430 and to ground conductor 380 when the operator is establishing a group conference. The select conference key SC is closed to control relays 430, 440 and 490 when the operator desires to select only certain of the subscribers in this group for conference;

Fig. 5 shows an operators cord circuit CC and diagrammatically illustrates the operators telephone circuit 500. The cord circuit comprises a ring answer key, a ring call key, and a talk key. A through key is associated with the operators common equipment for operating the switch through relay 550 in the cord circuit when it is desired to switch the talking conductor of the cord circuit straight through to establish a clean metallic circuit. A pair of relays 5|0 and 520 are associated with the answer plug of the cord circuit and are utilized for controlling the application of generator to an individual subscribers line and for controlling the answer lamp 532. The relay 5I0 is marginal and will not operate in series with the high resistance upper winding of relays, such as relays 360, 460 and 420. A similar pair of relays 560 and 510 are associated with the call plug of the cord circuit and perform similar functions. The relays 530 and 540 are connected in bridge of the cord circuit for feeding talking battery to the calling and called subscribers and for controlling the answer and call lamps 532 to 542, respectively.

In Figs. 6 and 7 are shown the detailed circuit arrangements for the common talking circuit and group signaling circuits for the lines in the restricted area. The common talking circuit indicated by the heavy lines terminate in the 010- erators switchboard in jacks GH, SGI to SG3, inclusive, and G2. The jack GH is used by the operator when it is desired to signal only the substation I0 at the guard house or to answer a call initiated by any one of the lines connected to this common talking circuit. The jack SGI and its associated relays 6I0 and B20 are for use when it is desired to signal the first group of substations comprising the substations II to I5, inclusive. The subgroup jack SG2 and its associated relays II0 and 120 are used by the operator when it is desired to select and signal only the second group subscribers, such as subscribers 2| to 25, inclusive. The subgroup jack SGB and its associated relays '|30 and |40 is used by the operator when it is desired to selectively signal and converse with the third group subscribers comprising the substations 3l to 35, inclusive. The group jack G2 and its associated relays and 760 is used by the operator when it is desired to signal all of the subscribers in the entire group. The signaling conductors SI1 and 6I8 for the rst subgroup of lines extend to the individual ringers RII to RIB of the first group subscribers and also to the ringer RIB in the guard house. 'I'he signaling conductors 'Ill and II8 for the second subgroup and the signaling conductors I3'I and 138 for the third subgroup are similarly connected to the ringers of the second and third groups, respectively, and to ringers in the guard house. The line circuit for this common talking circuit comprises the line relay 61|) and the cut-off relay 680.

Fig. 8 shows the detailed circuits of the conference circuit provided at the operators switchboard. This conference circuit comprises the conference jacks CJ I to CJ 5, inclusive, and the trunk jack TJ and associated relays 8I0 to 810, inclusive. The repeating coils RCI to RC5, inclusive, inductively connect the conference jacks with the common conference circuit to enable the operator to interconnect a plurality of groups of subscribers in a conference circuit.

In order to describe the operation it will be assumed that subscriber A in the administration building desires to converse with subscriber B also in the administration building. In response to subscriber A removing his receiver the following circuit is completed for line relay 330 in the individual line circuit LC-A for subscriber A: from ground through the upper winding of relay 330, contact 34|, back contacts 322, back Contact springs of switching key OS in the operations building, conductor 386 included in the cab-le extending to the administration building where conductor 386 terminates in back contacts 38| of switching key AS, line conductor 30| extending to the substation circuit A, through the switch hook contact at substation A and over line conductor 302 to back contacts 382 of switching key AS, conductor 381, back contacts 384 ofthe operations switching key OS, back contacts 324 and 344 and through the lower winding of line relay 330 to battery. Line relay 330 energizes and at contacts 33| completes the `circuit for brightly illuminating the call lamp L. This circuit'iay be traced from ground through the lower resistance winding of common night relay NR, back contacts 32|, contacts 33| and through lament of the lamp L to battery. Due to the lowl resistance of the common night relay NR the lamp L is relay 330 prepares a point in the locking circuit l for the conference relay 320. The night relay NR zs energized over the above traced circuit and at its contacts prepares the circuit for the night alarm NA which is only operative in case the night key NK is operated. The night relay NR is common to all of the line circuits LG-B, LC-C, LC-D, LC-E and LC-F.

Upon observing the brightly lighted lamp L the operator inserts the answer plug of her cord circuit CC into jack AJ I, thereby completing the circuit for energizing relays 340 and 520 in series as follows: from ground by `way of contacts 346, closed in response to the insertion of the plugr into jack AJ I lower winding of cut-off relay 340, sleeve of jack AJ I, sleeve conductor of cord circuit CC, contacts 525, winding of relay 528 and through the winding of marginal relay 5 I 8 to battery. Marginal relay 5|8 does not energize in series with the high resistance winding of cutoff relay 348. Relay 528, upon energizing, at contacts 52| prepares a point in the locking circuit for the switch through relay 558, and at contacts 522 prepares a point in the circuit for the answer lamp 532. Cut-oir relay 348, upon energizing over the above traced circuit, rst closes its contacts 342 to complete a locking circuit through its upper winding to grounded contact 346. At contacts 34| relay 348 opens the circuit extending to the upper winding of line relay 338, at back contacts 344 opens the circuit extending to the lower winding of line relay 338 and at front contacts 344 completes a point in the talking circuit including the heavy talking conductors. At contacts 345 relay 340 opens a point in the circuit for the upper winding of conference relay 320 and at back contacts 343 opens a point in the circuit for the lower winding of conference relay 328 while at front contacts 343 the lower winding of cut-01T relay 348 is short circuited thereby permitting the marginal relay 5|8 in the cord circuit to operate. Relay 5|8, upon energizing, at contacts 5| and 5|3, prepares points for connecting ringing currentl out over the tip and ring conductors of the answer plug of the cord circuit and at contacts 5|2 prepares a circuit for operating the answer lamp 532. The answer lamp 532, however, is not lighted at this time because the battery feed relay 538 in the cord circuit is operated over the following circuit: from ground through the upper winding of relay 538, back contacts 523 of the ring answer key, contacts 554, tip of cord circuit CC, tip of the jack AJ|, back contacts 322, back contacts 383, conductor 386, back contacts 38|, line conductor 38| through the substation circuit at substation A, line conductor 382, back contacts 382, conductor 381, back contacts 384l and 324, front contacts 344, ring contact spring of jack AJ l, ring of the cord circuit CC, back contacts 556, back contacts 526 and through the lower winding of battery feed relay 538 to battery. At contacts 53| relay 538 opens the circuit to the answer lamp 532 to prevent its illumination at this time. The operator now operates her talking key to bridge her headset across the talking conductors of the cord circuit at contacts 582 and 584. Contacts 583 completes a circuit (not shown) for connecting battery to the operators headset for talking purposes. The purpose of this arrangement is to provide the operator with a quiet headset when not in use. When the operator is informed by subscriber A that a Connection is desired to subscriber B the operator will restore the talk key and insert the call plug of her cord circuit into the jack AJ 2 individual to lineI B. In response to the insertion of the call plug in the jack AJ2 a circuit is completed for energizing the cut-off relay in line circuit LC-B, corresponding cut-off relay 340 in line circuit LC-A, and relays 568 and 518 in the cord circuit. Relay 518 is marginal and will not energize in series with the lower winding of the cut-off relay in line circuit LC-B. The circuit for energizing the cut-olf relay in the line circuit LC-B and relay 568 in the cord circuit may be traced as follows: from ground through springs, corresponding to springs 346, closed by the insertion of the call plug into the jack AJ2, through the lower winding of the cut-off relay in line circuit LC-B, over the sleeve of jack AJ2, the sleeve of the call plug of the cord circuit CC, contacts 565,

winding of relay 568 and through the winding of marginal relay 518 to battery. The cut-olf relay in the line circuit LC-B operates to perform the same functions as described for the cutoff relay 348 of line circuit LC--A. When the cut-oif relay in line circuit LC--B energizes it short circuits its lower winding to permit the energization of marginal relay 518. Relay 568, upon energizing, at contacts 56| prepares a locking circuit for the switch through relay 558 and at contacts 562 prepares a point in the circuit to the call lamp 542. Marginal relay 518 at contacts 51| and 513 prepares a circuit for connecting ringing current to the called subscribers line. At contacts 512 relay 518 completes a circuit for lighting the call lamp 542 as follows: from ground by way of contacts 512, 562 and 54| and through the filament of the call lamp 542 to battery. In the line circuit LC-B the cut-off relay has disconnected the associated line relay and has connected the conductors preparatory to ringing the called subscriber.

The operator now operates the ring call key to signal the called subscriber. In response t-o the operation of the ring call key, a circuit is completed at contacts 564 and grounded contacts 512 for maintaining relays 568 and 518 in operated position. At make contacts 566 and 563 of the ring call key the operator connects ringing current to the called subscribers line over the following circuit: from direct generator through contacts 513, make contacts 566, contacts 551, ring conductor of the call plug, ring spring of the jack AJ 2, front contacts of the operated cutolf relay, back contacts of the conference relay over the lower talking conductor extending through the switching keys indicated by the dotted lines, line conductor 384, through the ringer at substation B over line conductor 383 through the switching keys indicated by the dotted lines over the heavy upper talking conductor to a back contact on the conference relay, tip spring of the jack AJ2, tip conductor of the call plug, contacts 552, make contacts 563 and contacts 51| to ground. The operation of the ring call key opens contacts 565 thereby opening the original energizing circuit of the cut-off relay in line circuit LC-B, but this relay is maintained energized through its upper winding by way of the ground closed at the jack springs in response to the insertion of the call plug into jack AJ2. After ringing the called subscriber B, the operator restores the ring call key land when subscriber B removes his receiver battery feed relay 548 is energized over the following circuit: from ground through upper winding of relay 548, back contacts 563, contacts 552, tip conductor of the call plug, tip conductor of the jack AJ2, back contacts on the conference relay and thence over the heavy talking conductors previously traced for the ringing circuit back to back contacts on the conference relay, front contacts on the cutoff relay, ring conductor of jack AJ2, ring conductor of the call plug, contacts 551, back contacts 566 and through the lower winding of battery feed relay 548 to battery. At contacts 54| battery feed` relay 548 opens the circuit of the call lamp 542 thereby extinguishing the same to inform the operator that subscriber B' has answered the call. The calling and called subscribers now converse over the heavy talking conductors.

After conversation and in response to the replacement of the receiver at substation A battery feed relay 538 deenergizes and completes a circuit at contacts 53| for lighting the answer lamp A 532. This circuit may be traced `from ground at contacts |2 and 522, contacts 53| and through the filament of the answer lamp 532 to battery. When the called subscriber B replaces his receiver battery feed relay 540 deenergizes and at contacts 54| lights the call lamp 542 over the circuit previously traced. The operator upon ob. serving the lighted condition of these lamps removes the answer and call plugs from the jacks AJ and AJZ, respectively, thereby causing the deenergization of relays 5|0, 520, 56|] and 510 and the deenergization of the cut-oil relays in both line circuits LC-A and LC-B. All the ap- Daratus, including the relays, are now restored to normal position and may be used on subsequent calls. Connections between individual subscribers lines in any of the groups terminating at this switchboard may be completed in the same manner as described for the connection between subscribers A and B.

It will now be assumed that subscriber F desires to hold a conference with subscribers A and B simultaneously. Subscriber F removes his receiver to initiate a call and the operator answers this call by means of her cord circuit CC in the same manner as described previously for subscriber A. The cut-off relay in line circuit LC-F, corresponding to cut-oil relay 340, and relays 5|D and 526 in the cord circuit CC are operated in the same manner as previously described. When the operator is advised by subscriber F that both subscribers A and B are desired in a conference the operator will thereupon insert the call plug of her cord circuit into the subgroup jack SBI and will operate the group conference key GC. In response to the operation of the group conference key GC conductor 380 is grounded by contacts 429 and relay 430 is operated from grounded contacts 428. Relay 436, upon energizing, at contacts 43| to 436, inclusive, grounds the conductors, such as conductors 316, 316', 416 and 416 extending to each of the subscribers line circuits to provide a locking circuit for the associated conference relays. In response to inserting the call plug into jack SBI. relay 560, in the cord circuit and relay 366 are energized. The energizing circuit for relay 560 may be traced from grounded contacts 365, which were closed in response to the insertion of the plug into jack SBI, upper high resistance winding of relay 360, sleeve of jack SBI, sleeve of plug, contacts 565, winding of relay 56|) and through the winding of marginal relay 510 to battery. Due to the high resistance winding of relay 360, marginal relay 510 does not energize over this circuit. Another circuit for the lower winding of relay 360 may be traced from grounded contacts 365, normally closed contacts 352 and through the lower winding of relay 360 to battery. Relay 36|), upon energizing, at contacts 36| completes an obvious energizing circuit for relay 350 from grounded contacts 365. Relay 350, upon energizing, at contacts 35| completes a locking circuit for itself from grounded contacts 365 and at contacts 352 opens the circuit extending through the lower winding of relay 360. At front contacts 353 relay 350 connects battery potential to the windings of the ring cut-oil relays, such as relay 3|0, and at front contacts 354 connects grounded conductor 380 to conductor 315 for energizing the conference relays, such as relay 320 in each of the line circuits LC-A and LC-B. The circuit for conference relay 320 may be traced as follows: from grounded contacts 429, conductor 380, front contacts 354, conductor 315, contacts 326 and 345 and through the upper winding of conference relay 320 to battery. The conference relay in the line circuit LC-B is energized over grounded conductor 315 over a similar circuit. At contacts 32| relay 320 prepares a circuit for dimly lighting the lamp L, at iront contacts 322 and 324 prepares a point in the ringing and talking circuits, at contacts 323 prepares a locking circuit for the ring cut-off relay, and at contacts 325 completes a locking circuit for relay 320. This locking circuit may be traced from grounded conductor 316 by way of contacts 333, front contacts 325, contacts 345 and through the upper winding of conference relay 320 to battery. The operation of the conference relay in the line circuit LC-B performs similar operations.

The operator now actuates her ring call key to simultaneously signal both subscribers A and B. The operation of ring springs 563 and 566 are ineiective at this time because the marginal relay was not operated and therefor ringing current is not transmitted from the `corel circuit. However, in response to the opening of contacts 565, both relays 56|] in the cord circuit and relay 366 associated with the subgroup jack SB--l deenergize. In response to the deenergization` of relay 360 generator is connected to conductor 31| through the upper windings of cut-01T relay 3||D and the corresponding relay in the line circuit LCL-B through back contacts of these relays, over front contacts, such as contacts 322, over the conductors including the ringers at substations A and B, back over front contacts, such as contacts 324, and through back contacts, such as 3 5, to ground.

The restoration of the ring call key at contacts 565 again completes the circuit for reenergizing relays 560 and 360. At back contacts 362 relay 360 disconnects generator from the called lines and at front contacts 362 connectsA battery potential through resistance 363 to provide a circuit for energizing the ring cut-off relays, such as relay 3|0 in line circuits LC -A and LC-B when the subscribers A and B remove their receivers. When subscriber A removes his receiver ring cut-oir relay 3|0 is energized over the previously tracedringing circuit, this time, however, including the battery potential through resistance 363 instead of ringing generator included in the ringing circuit. When subscriber B removes his receiver the corresponding ring cut-off relay in the line circuit LC-B is likewise operated. Ring cut-oir relay 3|!) energizes and closes its contacts 3|2 to complete a circuit' for fully energizing and locking this relay through its lower winding. At back contacts 3|| relay 3|0 opens the circuit through the upper winding of ring cut-off relay and at front contacts thereof prepares a point in the talking circuit. At contacts 3|3 and 3|4 relay 3|0 connects the conference conductor 312 and 313 to the line conductors of subscriber A. At back contacts 3|5 relay 3|0 opens a further point in the circuit of ring cut-off relay and at front contacts thereof completes the talking circuit from the conference conductors 312 and 313 to the conductors of subscriber A. At front contacts 3|| and 3| 5 relay 3 0 completes the circuit for energizing line relay `33|) as follows: from ground through the upper winding of line relay 330, front contacts 3|| and 322 over the heavy talking conductors through the substation A, front contacts 324 and 3|5`and through the lower winding of line relay 330 to battery. The corresponding line relay in line circuit LC-B is also energized over a similar circuit. Line relay 33D, upon energizing, at contacts 33| completes a circuit for dimly lighting the lamp L and at contacts 332 completes a new locking circuit for the upper winding of conference relay 326. The .circuit for dimly lighting lamp L may be traced from ground through resistance R3, front contacts 32|, contacts 33| and through the filament of lamp L to battery. The lamp L is dimly lighted at this time to inform the operator that subscriber A has answered a conference call, The locking circuit for relay 326 may be traced from grounded contacts 332, contacts 325 and 345 and through the upper winding of relay 320 to battery. Conference relay 326 is now locked in energized position under control of the line relay 336 and is therefor independent of the previously traced locking circuit including the grounded conductor 316. Similar operations take place in the line circuit LC-B to connect the talking conductors of subscriber B to the conference talking conductors 312 and 313. Subscribers A and B are fed talking battery through the windings of their line relays, while the calling subscriber F is fed talking battery through the windings of battery feed relay 536 in the cord circuit CC. The talking circuit in this conference connection includes the talking conductors of subscribers A and B and extend by way of the heavy talking conductor through front contacts on the operated conference relays and operated ring cut-off relays to condensers C| and C?. and thence by way of conductors 312 and 313 to the tip and ring springs of jack SBI over the tip and ring conductors of the call plug of cord circuit CC, contacts 552 and 551, contacts 563 and 566 of the ring call key through condensers in the cord circuit, back contacts 523 and 526 of the ring answer key, contacts 554 and 556 over the tip and ring conductors of the answer plug of the cord circuit CC over the tip and ring conductors of the jack AJ5, back contacts of the conference relay, corresponding to relay 326 and over the line conductors 463 and 464 to line F'.

After both subscribers have answered thereby dimly lighting their associated lamps, such as L. the operator may restore the group conference key GC to disconnect ground from conductor 386 and to release relay 436. Relay 436, upon deenergizing, disconnects ground from conductors, such as conductor 316. After the conference is through and when subscriber F replaces his receiver the battery feed relay 530 in the cord circuit CC deenergizes to light the answer lamp 532 to inform the operator that subscriber F has hung up. When subscriber A replaces his receiver, line relay 336 deenergizes and at contacts 33| opens the cir- 5 cuit to lamp L which is extinguished. At contacts 332 relay 336 opens the locking circuit extending through the upper winding of conference relay to cause the deenergization of this relay. The conference relay deenergizes in this instance because the operator has restored the group conference key GC to remove ground from conductor 316. In case, however, the group conference key GC has been maintained energized the relay 436 grounds conductor 316 with the result that the locking circuit for the upper winding of conference relay 326 is transferred back to grounded conductor 316 when line relay 336 deenergizes. If subscriber A attempts to originate a new call, such subscriber will be connected back to the conference trunk conductors 312 and 313 because the ring'cut-off relay is locked in energized position as long as the conference relay is maintained operated. Since, however, the operator has restored the group conference key GC the subscriber A may at any time retire from the conference connection by replacing his receiver thereby causing the deenergization of his line relay 336 and his conference relay 326. In response to the deenergization of conference relay 326 the locking circuit of ring cut-off relay 3|6 is open whereupon this relay deenergizes and restores the line circuit LC-A to its normal condition. Assuming that subscriber A has replaced his receiver while subscribers B and F are still in conference, the above described operations take place and subscriber A can initiate a new call. It is, therefore, possible for any subscriber to retire from a conference connection after the group conference key GC is restored and initiates a regular call over their individual jacks, such as jack AJ I.

When subscriber B replaces his receiver, the relays in line circuit LC-B restore to normal in the same manner as described for line circuit LC-A. The lamp individual to line circuit LC-B is extinguished and the operator is therefore informed that the conference is now terminated. The operator therefore removes the cord circuit CC from jack AJ 6 and jack SBI thereby restoring relays 356 and 366 and relays 5|6, 526 and 566. All of the apparatus isnow restored to normal condition.

In case subscriber F desires to hold a conference with subscribers A, B, C, and D, the operator, after answering the call of subscriber 1T', and being informed that subscribers A to D, inclusive, are desired in the conference, the operator will operate the group conference key GC and insert the call plug of the cord circuit into subgroup jack SBZ and then rings these subscribers by operating the ring call key in her cord circuit. The operation of the group conference key GC again grounds conductor 386 and operates relay 436. Relay 436 grounds conductors, such as conductor 316 and 316 to prepare a locking circuit for the conference relays in the line circuits of the called subscribers. In response to inserting the call plug into jack SBZ relays 466 and 566 operate in the same manner as described for relays 366 and 566. Relay 456 is operated in response to the operation of relay 466 from ground at contacts 465 and 46|. At contacts 45| relay 456 locks itself to grounded conductor 465. At front contacts 453 relay 456 prepares the ringing circuit for the called subscribers and at front contacts 454 connects grounded conductor 386 to conductor 319 for energizing all of the conference relays, such as relay 326, in all line circuits LC-A to LC-D, inclusive. The circuit for energizing the conference relay 326 in line circuit LC-A may 'be traced as follows: from grounded contacts 429, conductor 386, front contacts 454, conductor 319, back contacts 354, conductor 315 and through contacts 326 and 345 through the upper winding of conference relay 326 to battery. Similar circuits are completed for operating the conference relays in line circuits LC B, LC--C and LC-D. The conference relays, such as relay 326, operate in the same manner as previously described and complete a locking circuit from grounded conductor, such as conductor 316, by way of contacts l325 and 345 and the upper winding of relay 326 to battery. Marginal relay 516 in the cord circuit does not energize in series with the high resistance upper winding of relay 466. In response to the operation of the ring call key, the circuit to relays 566 and 466 is opened at contacts 565 with the result that these relays deenergize and relay 466 at back contacts 462 connects generator to conductors 318 and 31| for simultaneously signaling subscribers A to D, inclusive. The ringing current extends from generator over conductor 364, back contacts 462, front contacts 453, conductor 318, by way of the multipled branches extending through the upper windings of the ring cut-oit relays in line circuits LC-C and LC-D and thence through the ringers at sub-scribers C and D back to ground in these line circuits. Ringing current is further extended by way of back contacts 353, conductor 31| through the upper windings of the ring cutoiT relays in line circuits LC--A and LC-B and out over the previously traced circuit including the ringers at subscribers stations A and B. When these subscribers answer their associated ring cut--oiv relays, such as relay 3|0, energize in the manner previously described to complete the circuits for energizing their associated line relays, such as relay 330. The energization of the line relays in the respective line circuits cause the lamps, such as L, to be dimly lighted to inform the operator that such subscribers have answered. After all oi these subscribers have answered the operator restores the group conference key GC and the conference relays, such as relay 326, are locked energized under control of their associated line relays. All of the subscribers are connected in the conference talking circuit, including conductors 312 and 313 and all subscribers A to D, inclusive, receive their talking battery from their associated line relays in a manner apparent from the foregoing description. After the operator restores the group conference key GC any one of the subscribers A to D, inclusive, may retire from the conference and initiate a new call if desired. After the conference is terminated the subscribers replace their receivers to cause the deenergization of their associated line relays to cause the lamps L to be extinguished. In response to the deenergization of the line relays, the conference relays and the ring cut-off relays in each of the line circuits deenergize to restore these line circuits to their normal condition. The operator now withdraws the plugs of her cord circuit and the apparatus is no-w restored to its normal condition.

In case some other line in another similar group, for instance a line in the operations building, desires to have a conference with all subscribers A to F, inclusive, in the administration building, the operator after answering the callwould then operate the group conference key GC, insert the call plug into the group jack GI and then ring these subscribers as previously described. The relay 436 is again actuated and grounds the conductors, such as conductor 316 in all the line circuits and conductor 380 is grounded in response to the operation of the group `conference key GC. Relays 4| 6 and 420 operate in the same manner and perform the same functions as described for relays 356 and 36D. Relay 4I|l, upon energizing, grounds conductors 419, 319 and 315 by way of grounded conductor 386 and contacts 4|4, 454 and 354 for energizing all of the conference relays, such as conference relay 320, in all of the line circuits LCL-A to LC*F, inclusive. A11 of the conference relays energize and lock to conductors, such as conductor 316, grounded by the actuation of relay 436. In response to the operation of the ring call key relay 42|) deenergizes to connect generator to conductors 418, 318 and 31|, thereby transmitting ringing current through the upper windings of the ring cut-off relays, corresponding to relay 3|0, over the line conductors of lines A to F, inclusive. When these subscribers answer, the ring cut-off relays operate over circuits similar to that previously traced now including front contacts 4|3 and 422, the resistance 424 to negative battery. When the ring cut-off relays in the respective line circuits operate, their corresponding line relays will actuate to dimly light their associated lamp, such as L, and to close a new locking circuit for the upper windings of the conference relays, corresponding to relay 326, in all of the line circuits in a manner similar to that previously described. After all of the subscribers have answered the operator restores the group conference key and the conference relays are then locked under control of their associated line relays. Any one of the subscribers can withdraw from the conference by replacing his receiver and may thereafter remove his receiver to initiate a new call. For example, when A replaces his receiver line relay 330 restores and at contacts 332 opens the locking circuit of the conference relay 326. Relay 320 restores and at contacts 323 opens the locking circuit of the ring cut-off relay 3| 0 which likewise restores. Line circuit LC-A is now restored to its normal condition and in case subscriber A removes his receiver the line relay 336 is operated to brightly light lamp L thereby informing the operator that subscriber A has retired from the conference and has initiated a new call. The operator is informed of the initiation of the new call by the brightly lighted lamp L since this lamp is only dimly lighted during the time subscriber A is included in the conference connection.

It will now be assumed that a particular subscriber desires to hold a conference with only certain of the subscribers shown in Figs. 3 and 4. It will be further assumed that only subscribers A, C and F are desired in this particular conference. The calling subscriber desiring such :a conference will initiate the call in the usual manner and will be answered by the operator and will in-y form the operator that a conference is desired with subscribers A, C and F. Since subscribers A, C, and F are in the administration building group, the operator will insert the call plug of her cord circuit into the group jack GI associated with the group of lines containing these subscribers lines. The operator now operates the conference select key SC and in so doing operates relays 430 and 446 over obvious circuits. Relay 43B, upon energizing, grounds all of the conductors corresponding to conductor 316 and relay 440, upon energizing, connects negative battery potential through the winding of relay 490 to all conductors corresponding to conductor 311 extending to the lower windings of the conference relays in each of the line circuits in this group. In response to the insertion or the call plug into the jack G| the relays 4|6 and 420 are operated as previously described. In this case, since conductor 380 is not grounded, the conference relays in the line circuits are not energized at this time. In order to condition the line circuit LC--A for connection with the conference circuit the operator will touch the tip of the call plug of the cord circuit with the sleeve of the jack AJ to complete an energizing circuit through the lower winding of conference relay 326. This circuit may be traced as follows: from ground through the upper winding of battery feed relay 540, back contacts 563 of the ring call key, contacts 552, tip conductor of the call plug, sleeve of the jack AJ I, back contacts 343', lower winding of conference relay 320, conductor 311, contacts 44|, and through the winding of relay 490 to battery. Since the subscriber C is desired in this conference the operator will tip touch the sleeve of jack AJ 3 to complete a similar circuit through the lower winding of the conference relay in the line circuit LC-3 to energize the corresponding conference relay. In a similar manner the operator tip touches the sleeve of the jack AJ 6 to operate the conference relay in line circuit LC-F. Conference relay 320 energizes over the above traced circuit to prepare the circuit for the lamp L, to prepare the ringing and talking circuits, to prepare the locking circuit for the ring cut-off relay 3I|J and to complete a locking circuit for itself. This locking circuit may be traced from grounded conductor 316, contacts 333, 325, 345 and through the upper winding of conference relay 320 to battery. The operation of the conference relays in line circuits LC-l-C and LC-F perform the same functions. Since the operator has tip touched only the sleeves of the jacks of subscribers A, C and F only the subscribers lines A, C and F are therefor prepared to be included in the conference circuit. After tip touching the sleeves of the jacks of subscribers A, C and F the operator inserts the call plug of the cord circuit CC into the group jack GI to operate relays 4|0 and 420 as previously described. The relay 490 is energized in series with the conference relay and at contacts 49| lights the lamp 492 during the interval that the operator is 'tip touching the sleeves of the desired subscribers desired in a conference. Relay 490 therefor energizes each time the operator tip touches a jack of an idle subscribers line in this group. The lighting of the lamp 492 informs the operator that the circuit has been completed for operating the desired conference relay. The relay 490 and the lamp 492 operate only during the time of tip touching the sleeves of the subscribers jacks to inform the operator that the corresponding subscribers lines are prepared for conference. In case the cut-olf relays, corresponding to cut-olf relay 340, were energized at the time the operator tip touched the jack AJ I, the back contacts 343 would be open with the result that no circuit is completed at this time for the lower winding of conference relay 326 or winding of relay 49|] and therefor the lamp 492 would not be lighted. Since the lamp 492 does not light at this time the operator is aware of the fact that the line circuit LC-A cannot be prepared for connection with the conference circuit. The energization of the conference relays in line circuits LC--A, LC-C and LC F prepare circuits for dimly lighting the lamps, corresponding to lamp L, prepares a locking circuit for ring cutoff relays, corresponding to relays 3H), and prepares the ringing and talking circuits in a manner similar to that previously described.

After insertion of the call plug into jack Gl the operator operates the ring call key to open the circuit of relay 560 at contacts 565. Relay 42|] deenergizes and at back contacts 422 connects the ringing current through the windings of the ring cut-oil' relays in only the line circuits LC-A, LC-C and LC-F. The ringing circuit from subscriber A extending from generator conductor 364, back contacts 422, contacts 4|3, conductor 418, back contacts 453, back contacts 353. conductor 31| through the upper winding of ring cut-off relay 3|!) and over the previously traced ringing circuit back to ground at back contacts 3|5. A similar ringing circuit is completed for line C from generator connected to conductor 318 over a branch circuit which extends to the upper winding 0f the ring cut-oil relay in the line circuit LC-C. A similar ringing circuit is provided for subscriber F and extends from a branch conductor connected to conductor 418 through the upper winding of the ring cut-off relay in the line circuit LC-F. After ringing and in response to the restoration of the ring call key in the cord circuit the relays 560 and 420 re-energize and the latter relay at front contacts 422 connects battery potential through resistance 424 to provide a circuit for energizing the ring cut-off relays when the calling parties remove their receivers. When subscriber A answers the call the ring cut-off relay 3|0 is operated from ground over the subscribers loop and through the upper winding of ring cut-oil relay 3|U to battery through resistance 424 as previously traced. Ring cut-off relay 3||l first operates its contacts 3|2 to complete a locking circuit through its lower winding and then operates its remaining contacts to connect subscriber A to the conference conductors 312 and 313 and to operate line relay 33|] in a manner similar to that previously described. At contacts 33| relay 330 dimly lights the lamp L and at contacts 332 completes the locking circuit including contacts 325 and 345. for the upper winding of conference relay 326. In a similar manner the ring cut-off relays and the line relays in line circuits LC-C and LC-F operate when subscribers C and F remove their receivers in answering this this call. Subscribers A, C, and F are now each connected to the conference conductors 312 and 313 and may now converse with each other and with the calling party. The talking battery for the called subscribers extend through their individual line relays, corresponding to line relay 330. After all of the desired called subscribers are included in the conference circuit, the operator may restore the select conference key SC to cause the deenergization of relays 430 and 446. The operated conference relays are now maintained in energized position under control of their respective line relays as previously described. Any one of the subscribers A, C or F may retire from the conference and initiate a new call by simply replacing his receiver and removing the same. When the receiver at subscriber A is replaced line relay 330 deenergizes and at contacts 33| lamp L is extinguished. On the termination of the conference the calling and called subscribers replace their receivers to restore the line circuits to their normal condition as previously described thereby extinguishing the lamps, such as lamp L. The operator thereupon removes the plugs of her cord circuit from the jacks of the calling and from jack GI to restore the relays in the cord circuit and to restore relays 4|0 and 420. All the apparatus is now restored to normal and may be used on subsequent calls.

Referring now to the common talking circuit shown in Figs. 6 and 7 it will be assumed that subscriber ID at the guard house desires to call another subscriber, for example, subscriber A in the administration building. Responsive to the removal of the receiver at substation Il), line relay 610 is energized over the following circuit: from ground through the upper winding of line relay 610, back contacts 68 I, through the line switching keys in the operations and administration buildings, conductor 69|, through substation I0. conductor 692 through the administration and operations building switching keys, back contacts 684, and through the lower winding of line relay 610 to battery. At contacts 61| line relay 616 lights the lamp LI to indicate to the operator that some one of the subscribers on this common talking circuit has initiated a call. Upon observing the lighted condition of the lamp LI the operator inserts the answer plug of her cord circuit CC into jack GH. In response to the insertion to the answer plug into jack GH relays 686 and 520 are operated over the following circuit: from ground at spring 685, lower winding of relay 686, sleeve f jack GH, sleeve of the answer plug, contacts 525, through the windings of relay 526 and relay |6 in series to battery. Relay 5I6 is a marginal relay and will not energize in series with the lower winding of relay 680. Relay 686, upon operating, first completes a locking circuit through its upper Winding over contacts 662 from grounded contacts 685 and then short circuits its lower winding at contacts 683 to permit the operation `of marginal relay 5I6 in the cord circuit. Relay 686 at back contacts 68| and 684 disconnects the line relay 616 and at front contacts 684 completes the talking circuit and the circuit for operating the battery feed relay 536 over the heavy talking conductors including the tip and ring conductors `of the jack GI-I and the Cord circuit CC. The battery feed relay at contacts 53| extinguishes the answer lamp 532 in case it has been illuminated. Line relay 610, upon deenergizing at contacts 61| extinguishes the lamp LI.

When the operator is advised that a connection to subscriber A is desired, the operator inserts the call plug of the cord circuit CC into jack AJ I and rings subscriber A as previously described by the operation of the ring call key and the application of generator to contacts 513 and 566 of the cord circuit. The connection to subscriber A is completed as previously described. Talking battery is fed through the windings of the battery feed relays 536 and 546 for the calling and called subscribers respectively. After termination of conversation and responsive to the subscribers re placing their receivers, battery feed relays 536 and 546 deenergize and light their associated call and answer lamps 532 and 542 to inform the operator that the connection is no longer desired. The operator now removes the cord circuit from the jacks GH and AJ I to restore the relays in line circuit LC--A to normal and to restore relay 686 in the line circuit of the common talking circuit. The line relay 616 in the line circuit of the common talking circuit is again normally connected to line conductor 69| and 662 in response to the restoration of cut-off relay 686.

Any other subscriber on this common talking circuit can initiate a call in the same manner as described for subscriber I6 since all of the subscribers are connected to the common talking conductors 69| and 692.

It will now be assumed that subscriber I6 at the guard house is called by subscriber A. When the operator is informed by subscriber A that subscriber I6 at the guard house is desired she will insert the call plug of her cord circuit into jack GH. Relay 686 and relay 566 are now energized over the following circuit from ground by way of contacts 665, lower winding of cut-off relay 636, sleeve of jack GH and the call plug, contacts 565, winding of relay 566 and through the winding of marginal relay 516 to battery. Relay 516 will not energize in series with the lower winding of relay 686. Relay 686 energizes and rst locks itself to contacts 682 and 685 and then short circuits its lower winding at contacts 683. At back contacts 68| and 684 relay 686 disconnects the line relay 616 and at front contacts 684 completes a point in the talking circuit. Marginal relay 516 energizes when cut-off relay short circuits its lower winding and a circuit is now completed for lighting the call lamp 542 by way of contacts 51.2, 562 and 54|. The operator now operates the ring call key to connect generator from the cord circuit to the called line. The relays 566 and 516 in the cord circuit are maintained in operated position by way of contacts 516 and 564 when the ring call key is 0perated. Ringing current is connected to the call line through the ring call key as follows: from generator, contacts 513, front contacts 566, contacts 551 over the ring conductor of the cord circuit CC and jack GH, front contacts 664, through the switching keys to conductor 692 through the ringer RI6 at the guard house, over conductor 69| through the switching keys over the tip conductor of the jack GH and the call plug of the cord circuit, contacts 552, front contacts 563, to ground at contacts 51|. After ringing the operator restores the ring call key and when subscriber I6 responds the battery feed relay 546 is energized by Way of back contacts 563 and 566 and the called subscribers loop.. At con-` tacts 54| relay 546 extinguishes the call. lamp 542 to notify the operator that subscriber I6 has answered the call. After conversation and responsive to the calling and called subscribers replacing their receivers, battery feed relays 536 and 546 restore to light their associated answer and call lamps 532 and 542, respectively. 'I'he operator now withdraws the plugs of her cord circuit from the jacks and returns the apparatus to normal position.

As previously described, the remaining lines in the restricted area are divided into three groups of lines each having separate signaling conductors. It will now be assumed that the subscribers II to I5, inclusive, in the rst subgroup are desired in a connection. Afterl answering a call and being informed that one or all of the subscribers in the first group, comprising lines II to I5, inclusive, are desired in a connection, the operator inserts the call plug of her cord circuit f CC into jack SGI and then actuates the ring call key. In response to the insertion of the call plug into jack SGI relaysl 626 and 566 are operated over the following circuit: from ground by way of contacts 625 through the upper high resistance winding of relay 626, sleeve of jack SGI, sleeve of the call plug, contacts 565, winding of relay 566 and through the winding of marginal relay 516 to battery. Marginal relay 516 will not operate in series with the high resistance winding of relay 626. A branch circuit also extends by way of contacts 6I3 through the lower winding of relay 626 to assist this relay in operating. At contacts 62| relay 620 completes a circuit from grounded contacts 625 through the lower winding of relay 6I6 to operate the latter relay. At contacts 622 and 623 relay 626 disconnects ground and generator. Relay 6I6 at contacts 6| 4 completes a locking circuit for itself from grounded contacts 625 and at contacts 6 I 5 and 6 I 6 prepares a point in the signaling circuit which is now open at contacts 622 and 623. At contacts 6II and 6|2 relay 6I6 completes a circuit for energizing cut-off relay 686 through the upper windingof relay 6l6 as follows: from ground by way of contacts 6II, lower winding of relay 686,l contacts 6|2 and through the upper winding of relay 6|6 to battery. Cut-olf relay 686- operates and first closes a locking circuit for itself by way of contacts 682 and 6I I and then short circuits its lower winding at contacts 683. At contacts 68| and 684 cut-off relay 680 disconnects the line relay 610 and completes a point in the talking circuit.

In response to the operation of the ring call key, relays 560 and 620 deenergize when contacts 565 in the ring call key are opened. The deenergization of relay 566 in the cord circuit is without eiect at this time because the marginal relay 510 is not operated. Relay 620 deenergizes and at contacts 622 and 623 connects generator and ground to signaling conductors 6 I 'I and 6I8, respectively, to operate all the ringers RII to RIG. inclusive. The ringer RI6 located at the guard house is operated whenever ringing current is transmitted over the signaling conductors 6I1 and 6I8 for the first subgroup of subcribers in this restricted area. When any one of the subscribers answer and close a bridge across the conductors 69| and 692, the battery feed relay in the cord circuit is operated. The talking circuit for the called subscribers may be traced as follows: from ground and battery through the windings of battery feed relay 540, back contacts 563 and 566 of the ring call key, contacts 552 and T, tip and ring conductors of the call plug and jack SGI. over the heavy conductors through contacts 684 and the switching keys, over the common talking conductors 69| and 692 to the called substations. After conversation and when the calling subscriber replaces his receiver the operator receives disconnect supervision in response to the deenergization of relay 53|] by the lighting of the answer lamp 532. The operator now removes the cord circuit from the jacks of the calling line and jack SGI to restore the relays in the cord circuit CC and relay 6I0, 620 and 680.

In case one or more of the subscribers in the second subgroup are desired in a connection the operator would plug into jack SG2 and operate the ring call key as before. In this case relays 120, 'H0 and 686 are operated in a manner similar to that described when calling the first subgroup. In response to the operation of the ring call key relay deenergizes to connect generator and ground to the signaling conductors 'H1 and 1I8, respectively, to operate the ringers R2I to R26, inclusive. subgroup of subscribers, the operator plugs into jack SGB to operate relays lil, 140 and 680 over similar circuits. In response to the operation of the ring call key relay deenergizes and connects ringing current to the signaling conductors 131 and 738 to operate the subscribers ringers R3I to R36, inclusive. The guard house is provided with four ringers, an individual ringer RI IJ. a ringer RIB which is operated whenever the first subgroup is signaled, a ringer R26 for the second subgroup and a ringer R36 with the third subgroup. In case it is desired to signal all of the subscribers in the restricted area, the operator would plug into jack G2 and operate the ring call key. Relays 150, and 680 are operated in a manner obvious from the foregoing description and in response to the actuation of the ring call key relay 160 deenergizes and connects generator and ground to each of the three signaling circuits to thereby simultaneously ring all the ringers RII to R36, inclusive.

Any subscriber on the common talking circuit can originate a call and request a connection to any other subscriber connected to this common talking circuit. For example, it will be first asfr i In order to signal the third LIS sumed that subscriber II desires a connection with the subscriber I0 at the guard house. In response to the removal of the receiver at substation I I, the line relay 610 is operated to light lamp LI to signal the operator who then inserts the answer plug of her cord circuit into jack GH. In response to the insertion of the answer plug into jack GI-I cut-01T relay 680 and relay 520 operates and after relay 686 short circuits its lower winding marginal relay 5I0 operates Relay 530 is operated over the calling loop to open the circuits to the answer lamp 532. When the operator is informed that subscriber I0 is desired she will advise the calling subscriber II to momentarily replace his receiver while she is ringing subscriber IIl. When subscriber I I replaces his receiver relay 530 deenergizes to light lamp 532. The operator now operates her ring answer key to operate ringer` RIU. At contacts 524 relays 5 I 0 and 520 are maintained in operated condition when the sleeve circuit is opened at contacts 525 and relay 680 is maintained operated over its upper winding to ground at contacts 685. At front contacts 523 and 526 ringing current is transmitted by way of contacts 5|3 and the heavy talking conductors to operate ringer RI 0. After ringing the operator restores her ring key and when subscribers IIJ and I I remove their receivers battery feed relay 530 is orated to extinguish the lamp 532, The talking current for subscribers I0 and II is furnished through the windings of battery feed relay 530. After conversation and when both subscribers replace their receivers. relay 530 deenergizes and lights the answer lamp 532. The operator now removes the plug from jack GH and all apparatus is restored to normal.

In case subscriber II desires to converse with subscriber 2|, subscriber II will initiate the call and operate the line relay 610 to light lamp LI in order to signal the operator. The operator answers the call in the usual manner by inserting the answer plug of her cord circuit CC into jack GI-I. Relays 686, 526, 536 and 5l!) energize and line relay 610 deenergizes as previously described. When the operator is informed that subscriber 2I is desired in a connection she will insert the call plug of the cord circuit in use, or a plug of another cord circuit, into jack SGZ and operate the associated ring call key of such cord circuit. In response to the insertion of the call plug into jack SG2 relays 'I I0, 120 and 560 operate as previously described. Marginal relay 510 does not operate because of the high resistance upper winding of relay 126. The operator now operates her ring call key to open the circuit of relay 126 which accordingly deenergizes and connects ringing current to the signaling conductors III and 'H8 to operate ringers RI t0 R26, inclusive, It will be seen that all of the subscribers ringers in the second subgroup as well as the ringer R26 associated with the guard house are operated. These subscribers may remove their receiver and may replace them when informed by the calling subscriber the message is intended for subscriber 2 I After ringing over the signaling conductors the operator will withdraw the call plug from jack SGZ leaving only the answer plug of her cord circuit in jack GH. Talking battery is fed through the windings of the battery feed relay 530 over the heavy talking conductors of the cord circuit and the heavy talking conductors of the common talking circuit. After conversation and in response to the subscribers replacing their receivers battery feed relay 530 deenergizes to light the lamp 532 thereby advising the operator that this conversation has been terminated. The operator then withdraws the plug from jack GH to restore the apparatus to normal.

In case subscriber II desires to talk to a subscriber in his own subgroup, for example, subscriber i2, the call will be initiated and answered in the same manner as previously described and in order to signal subscriber I2 the operator will insert the call plug of her co'rd circuit into jack SGI and operate her ring call key. The relays 6 I 0, 620 and 56D operate in a manner obvious from the foregoing description and when the operator o-perates her ring call key relay 620 deenergizes to connect ringing current to the signaling conductors S I 1 and BIB to simultaneously operate ringers RII to RIB, inclusive. After ringing the operator withdraws the plug from jack SGI leaving only her answer plug in jack GH, After conversation and in response to the subscribers replacing their receivers the established connection is released in the same manner as previously described.

The subscriber IU at the guard house may also originate a call and have the operator selectively signal only a certain one of the subgroups or may have the operator simultaneously signal all of the subscribers in all three subgroups by insertion of the call plug into group jack G2. In case subscriber II) desires to simultaneously signal all of the subscribers in all three subgroups, the operator, after answering the call, will insert the call plug into jack G2 and operate her ring call key to deenergize relay 160 in a manner obvious from the foregoing description. In response to the deenergization of relay 16B ringing current is simultaneously connected to all three of the signaling circuits comprising conductors SI1, 6I8, 1I1, 1| 8, 131 and 138 to simultaneously operate all of the ringers RII to R36, inclusive. After ringing the operator will withdraw the call plug from jack G2 and talking battery for the subscribers lines is furnished through the battery feed relay 530. The release of the established connection is the same as previously described.

The conference circuit shown in Fig. 8 is provided for use when it is desired to connect a plurality of lines in a plurality o f different groups in a conference connection. For example, some executive, having an individual line, may desire a conference with only certain of the lines in the administration building, or all these lines, and at 7' the same time have included in this conference all or only certain of the lines in the operations building, all or only a portion of the lines in the boundary group, as well as all or only a portion of the lines in the runway group.

It will first be assumed that the calling line desires a conference connection including all of the lines in the administration building and all of the lines in the boundary group. The call is answered by the operator in the usual manner by plugging into the jack of the calling line and upon being advised that the conference should include all the lines in the group of the administration building and the boundary group, the operator will insert the call plug of the cord circuit in use into conference jack CJ I. In response to the insertion of the call plug into jack C'JI relay Blll is operated by the closure of the jack springs BIG. At contacts 8| l relay 8H) completes the talking circuit to the lefthand windings of the repeating coil RCI and at contacts 8| 3 removes the resistance shunt around the righthand windings of repeating coil RCI. At contacts 8I2 relay 8I0 completes the circuit for operating relay 560 of the cord circuit as follows: from ground through resistance 8M, contacts 8I2, sleeve of jack CJ I, sleeve of call plug of cord circuit CC, contacts565, winding of relay 560 and through the winding of marginal relay 510 to battery. Relay 510 is marginal and will not energize in series with resistance 8 I4.

The operator now takes another cord circuit, similar to cord circuit CC, and inserts the answer plug into group jack GI and operates the group conference key GC associated with the group of lines in the administration building. In response to the insertion of the answer plug into jack GI relays 4I0, 420 and 520 operate in a manner apparent from the foregoing description. Conductor 380 is grounded and relay 430 operates to ground conductors, such as conductor 316, in response to the operation of the group conference key GC. At contacts 4M relay M0 grounds conductor 419 thereby grounding conductors corresponding to conductor 315, to cause the energi- Zation of the conference relays, corresponding to relay 320, in all of the line circuits of the administration group. These operated conference relays prepare the circuits for the individual ring cut-off relays, such as relay 310. 'Ihe operator then inserts the call plug of this other cord circuit into jack CJ 2 to operate relay 820 which performs the same functions as stated for the corresponding relay GIU. The operator now takes a third cord circuit and plugs it into the group jack BG of the boundary group and into conference jack CJ3 and operates the group conference key, such as GC, associated with the boundary group to perform operations similar to that described for the administration group. In case any further groups are desired in the conference, the operator would use another cord circuit and plug it into the corresponding group jack and one of the conference jacks and operate the corresponding group conference key. After the operator has plugged up the desired number of conference connections she will then operate the ring keys in all but the first cord circuit to simultaneously signal all of the subscribers in their respective groups. For example, when the ring answer key in the second cord circuit is actuated relay 420 deenergizes and simultaneously rings all the subscribers in the administration group in the same manner as previously described. All of the boundary lines are simultaneously signaled in a similar manner, When each of the subscribers respond, their associated individual ring cut-off and line relays, corresponding to relays 3I0 and 330, respectively, operate to complete the talking circuits over the heavy talking conductors, to dimly light their individual lamps, corresponding to lamp L, and to lock their associated conference relays, corresponding to relay 320 under control of their line relays. After all of the subscribers in a group have answered the operator may restore the group conference key for that group. The individual conference relays will now be maintained in operated position by their associated line relays. Talking battery for the called subscribers lines are fed through the windings of their individual line relays. The talking circuits include the heavy talking conductors extending from the subscribers lines, the group conference conductors, such as conductor 312 and 313, in the administration and boundary groups, the heavy talking conductors of the cord circuits and the conference circuit in Fig. 8. Talking currents are induced through the windings of the repeating coils RCI, RC2 and RC3 in a well known manner. After the operator restores the group conference keys any one of these subscribers may retire from the conference and initiate a regular call in a manner apparent from the foregoing description.

When the calling subscriber replaces his receiver after termination of the conference the battery feed relay 530 of the rst cord circuit deenergizes to give the operator disconnect supervision by lighting lamp 532 and in response thereto the operator withdraws the various plugs from the group and conference jacks as well as from the calling line jack. The operated relays are all restored to normal.

In case only certain individual subscribers lines are to be connected to the conference circuits then the operator would plug into their corresponding individual jacks and in such cases the 'operator would receive disconnect supervision from such lines when they replace their receivers.

From the foregoing it can be seen that the conference circuit may be connected to as many groups of lines as there are conference jacks provided.

It will now be assumed that a calling subscriber desires a conference with only certain of the lines in a plurality of different groups of lines. For example, it will be assumed that the calling subscriber desires subscribers A and F in the administration group and two lines in the boundary group, which terminates in jacks BJI and BJ 2, in a conference. After answering the call the operator inserts the call plug of the rst cord circuit into the conference jack CJ I, then inserts a second cord circuit into jack GI and operates the select conference key SC associated with the administration group. The operator then tip touches the sleeves of jacks AJ I and AJ 6 with the tip of the call plug of the second cord circuit to operate and lock the conference relays, corresponding to relay 320 in both line circuits LC-A and LC-F. After this the operator inserts the call plug of the second cord circuit into jack CJ 2. In a similar manner the operator takes a third cord circuit and inserts it into the boundary group jack BG, operates the associated conference select key, and then tip touches the sleeve of jacks BJ I and BJ 2 with the tip of a call plug of the second cord circuit and thereafter inserts this plug into the third conference jack CJ3.

The conference relays, corresponding to relay 320,

in the line circuits individual to these subscribers are locked in energized position. The manner in which these conference relays are energized may be briefly described as follows: when the conference key is actuated battery potential through the winding of relay 490 is connected through the lower windings of the conference relays, such as relay 320, and when the grounded tip of the cord circuit touches the sleeve of the jack the conference relay energizes and locks to ground conductor, such as conductor 316 through its upper winding.

After completing these operations the operator operates the ring answer keys in the second and third cord circuits to deenergize the group relays, corresponding to relay 420. These relays deenergize and connect ringing current through the windings of the ring cut-off relays to the selected lines by way of the operated contacts, such as contacts 322 and 324, on the energized conference relays. When each called subscriber answers his individual ring cut-off relay and line relay operate and the latter relays dimly light the call lamps and locks the conference relays independent of the operated condition of the select conference key. After all of the selected subscribers have answered the operator may restore the select conference keys to normal. The talking circuit over which these subscribers converse includes the heavy talking conductors and repeating coils RCI, RC2 and RC3 as previously described. Any one of the called subscribers may retire from this conference connection and in itiate a regular call as previously described. After termination of the conference and when the calling party replaces his receiver the operator receives disconnect supervision in the usual manner and releases the connection.

It should possibly be stated that the trunk jack TJ is connected to 'the conference circuits o-f Fig. 8 to provide a means for including a, trunk connection in the conference circuits or an additional subscribers line. Relay 810, as is obvious, operates when the plug is inserted into jack TJ and this relay at contacts 81| removes the shunt from around condensers C6 and C1. At contacts 812 relay 870 connects ground through resistance 813 to operate relays 520 or relay 560 dependent upon which plug is inserted into trunk jack TJ. The marginal relays in the cord circuit will not operate in series with resistance 873.

It is apparent from the foregoing description that the conference circuits may be connected to any of the lines in the runway, boundary, administration, or operations group or to any individual lines not included in such groups. It is also apparent that when a conference between a calling line and two or more lines of a certain group is desired that the conference circuits of Fig. 8 are not needed since such a conference connection can be set up in the group conference circuits provided in such certain groups. Therefore, the conference circuits of Fig. 8 are only used when a number of subscribers in different groups, or individual subscribers not in any groups, are desired in a conference.

Having described the invention, what is considered to be new and is desired to have protected by Letters Patent will be set forth in the following claims.

I claim:

1. In a telephone system, an operators position, a group of subscribers lines each normally terminating in an individual jack at said position, a talking circuit common to all said subscribers lines in said group, a group jack terminating said common talking circuit at said position, a group conference key associated with said group jack, and means jointly responsive to the insertion of an operators cord circuit into said group jack and the actuation of said group conference key for disconnecting each of said subscribers lines from its individual jack and for preparing the connection of each of said subscribers lines to said common talking circuit.

2. In a telephone system, an operators position, a group of subscribers lines each normally terminating in an individual jack at said position, a talking circuit common to all said subscribers lines, a group jack terminating said common talking circuit at said position, a group conference key associated with said group jack, a conference relay individual to each subscribers line, means including a circuit jointly controlled by the insertion of an operators cord circuit into said group jack and by the actuation of said key for operating all said conference relays, and means controlled by the actuated conference relays for operatively associating said common talking circuit with said subscribers lines. 

